In the fabrication of structural members, such as wide flange beams, channels, angles, tube and plate it is necessary to drill holes at specified positions in the various surfaces of the members and the location of the holes will vary from piece-to-piece. To automate the drilling operation, multiple head drilling machines have been developed. Machines of this type are generally composed of an upper spindle assembly and a pair of side spindle assemblies. Each assembly carries one or more drill heads that can be positioned to drill holes at desired locations in the web and flanges, or other surfaces of the structural member as the member is fed through the machine.
In the conventional multiple head drilling machine the drilling heads are each carried by a spindle which is mounted for rotation, as well as for axial movement in a spindle block, and one or more spindle blocks are mounted in parallel relation in the assembly. In the past, for each run it was necessary to disassemble the assembly of spindle blocks and manually reposition the spindle blocks in the desired location for the next succeeding run.
To eliminate the manual labor involved in setting up the spindle block assembly, systems have been developed in which the spindle blocks in each assembly are connected to a lead screw, so that rotation of the screw in one direction will move the blocks and spindles toward each other, while rotation of the lead screw in the opposite direction will move the blocks spindles away from each other. A second lead screw, or screws, moves a given group of spindle blocks simultaneously as a set in one direction or another. However, machines of this type have no provision for individually and automatically moving each spindle block.